Homework tonight:
Research Geological Time and write about it in your booklet.
Geological time - Earth's 4.5 billion years is broken down into periods of thousands, millions, and billions of years, based on when certain organisms or geological events dominated Earth’s development.
The fossil record evidences, or shows us, that the types of organisms alive on Earth have changed greatly over time. For example, the group of animals called dinosaurs lived from about 235 mya, or million years ago, until about 65 mya. Another example: the earliest animals recognized as having human characteristics, known to us as Homo erectus, lived in Africa and Asia between about 1.89 million and 143,000 years ago.
"The Earth formed about 4.6 billion years ago and the earliest forms of life are thought to have appeared approximately 3.5 billion years ago
- To describe the geology and history of life on Earth, scientists have developed the Geological Time scale. [See a graphic example at https://socratic.org/questions/what-percent-of-earth-s-history-did-dinosaurs-live ]
The geological time scale measures time on a scale involving four units:
- An epoch is the smallest unit of time on the scale, but still encompasses a period of millions of years.
- Chronologically, epochs are grouped together into larger units called periods.
- Periods are combined to make a subdivision called an era.
- An eon is the largest division of geological time.
[Or, listed from largest to smallest, each Eon is made up several eras, which are made up of several Periods, which are made up of several epochs].
The division of time units in the scale is typically based on the occurrence of a significant geological or biological event (e.g. mass extinction).
- So, geological time categories change in length and do not usually consist of a uniform length of time."
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